In April 2003, Marvel will raise the price of many of its titles from $2.25 to $2.99. This price rise will affect 13 regular titles. The only Spider-Man title that will be affected at the moment is Spider-Girl. The price hike will start with issue #59.
The main reason that Marvel has given for raising the price on these titles is that they aren't selling well enough. Thankfully, most of Spidey's titles at the moment are top sellers!